Process of making wood pulp



Patented Feb. 23,1932

- UNITED STATES PATENT OFFICE WILLIAM BRYDGES AND SPOTTSWOOD G. FOSTER, OF BIG ISLAND, VIRGINIA, ASSIGNORS TO BI'HJFORD PULP & PAPER COMPANY, INC., OF. BIG ISLAND, VIRGINIA, A GOR- IPORATION OF VIRGINIA PROCESS OF MAKING WOOD PULP No Drawing.

Our invention relates to new and useful improvements in the process of makin wood pulp for paper making, molded and kindred purposes, and more particularly to the treatment of pulp wood and the manufacture of what is known in this art as mechanical pulp.

One of the principal objects of the invention resides in the provision for the treatment of pine wood and other coniferous woods before it is reduced to a pulp by the usual mechanical methods.

Another object of the invention is to produce means to facilitate the mechanical separation of the wood fibres and to generally improve the properties of the wood pulp from which the paper is made, so that a stronger sheet of paper or other product may be produced than would be produced from ground wood pulp or from steamed ground wood pulp.

Still another object of the invention is to provide a method which, through its treatment of the wood, will facilitate the control of the penetration of moisture of the paper made from the pulp, so that the paper produced from said pulp will take up more readily the moisture of the steam which is implnged upon the surface thereof while the said paper is being run through a machine for crimping, corrugating, folding or other-.

wise deformed, without rupturing, tearing, crushing or injuring the paper sheet.

The present application is similar in' its broadest aspect to the process of making wood pulp set forth in Letters Patent, No. 1,737,542, granted to us on November '26, 1929.

We have found that by subjecting the wood at a certain time to a vacuum treatment,

- which will be more fully described as the application proceeds, the wood will be more thoroughly penetrated with water and alkali and especiallythe heart wood, so that the resulting pulp will be more uniform in quality while the losses from fine and coarse material will be greatly reduced. Furthermore, the pulp, molded products or kindred articles are more uniform in texture, strength and flexibility and, when deformed or crimped Application filed July 16,

1931. Serial No. 551,289.

on corrugating or other machines, the resulting deformed sheets will be stiffer and will not crack.

Still another object of the invention, therefore, is to provide a method for treating the Still another object of the present inven= tion is to treat the wood for pulp by controlling the saturation of the steam into the vessel which encloses the wood and by the injection of water or weak alkali liquor into the tank while the wood is undergoing a steaming process and the creating of a vacuum in the vessel which so improves the penetration of the wood that the time ordinarily required for the immersion treatment is greatly reduced, and with wood under certain conditions and for pulp of certain qualities, .it is possible to eliminate entirely the immersion treatment,

With these and numerous other objects in view, our invention consists in the steps in the process hereinafter and more particularly setforth.

In carrying out our improved process, .we preferabl utilize a spherical tank which will withstan considerable steam pressure, and we have found in actual practice that a tank, say built for one hundred pounds pressure and whose volume is about fourteen hundred and, thirty-six cubic feet, is most desirable; Within this tank are placed the bolts or blocks of/t vood which are to be used for the making of the pulp and the average volume of solid wood used is about six hundred and seventy-five cubic feet. This tank is also filled with a quantity of alkaline solution, such as soda ash, lime, or the like, whereupon steam is admitted to the tank.

The pressure of the steam is raised acconding to the size and condition of the wood and the length of time the steam pressure is maintained therein depends on the size and condition of the wood. The wood in this alkaline solution is then cooked and while being so cooked the gases are vented off and some of the crude oils from the wood may be recovered for commercial use in the usual or preferred manner. This alkaline liquor and condensate may be drained off before the end of the steaming process, according to the size and condition of the wood. Thus far, the method or'process'is similar to that outlined in the aforementioned patent.

This cooking treatment continues for the desired length of time, according to the size and condition of thewood and, when completed and the tank emptied of the liquor.

contents, the tank is then filled with cold water. This cold water condenses the steam, thereby creating a partial vacuum.

We have found that if there are about six hundred and seventy-five cubic feet of wood in the tank, the steam space in the tank will be seven hundred and sixt -one cubic feet at the time the water is admitted which, at twenty-five pounds gauge pressure, has a weight of 75.5 or equal to 8.7 gallons of water. Therefore, to condense this steam it will require about one hundred gallons of water, depending on the temperature of the water. This would create and maintain a vacuum until all of the space, that is about six hundred and seventy-five cubic feet, is filled with water.

The temperature of this water may vary with seasons and may be from 32 F., average about 60 F. to F. The lower the temperature of the water at the time of intro- ,duction, the hi her the vacuum. This vacuum has been 0 served to be as high as eight to'ten inches.

Also, we have found that for the treatment of certain qualities of pulp, it may be desirable, after steam has been applied to the tank and maintained for a predetermined length of time to cook the wood, to then exhaust the gases and recover the crude oils from the tank and drain the tank of all its liquors while the steam pressure is still kept. Then, further water or weak liquor is injected into the tank while this steam pressure is still being maintained. While the saturated steam is being admitted to the tank, the excess water, condensate or weak liquors'may be drained off to control the saturation of the steam and the wood will then be more thoroughly penetrated which will, of course, minimize the length of time required for the immersion process.

\ We have also found that the wood, having been subjected to heat, is expanded, and when this partial vacuum is created the water penetrates the wood more rapidly and more thoroughly and especially the heart wood,

thus making the penetration of the wood more uniform.

To maintain and increase this vacuum, a steam jetair ejector or vacuum pump of any usual type might be connected to the aboveenclosed tank and this vacuum process may be continued, according to the size and condition of the wood and the degree of penetration required. Now the water may then be kept in the said enclosed tank a number of hours and the required temperature and the pressure of the water maintained in the tank, according to the size and condition of the wood under treatment.

The treatment of the wood with warm water is known as an immersion treatment and is for the purpose of washing the wood of alkali, resinous matters and other substances and also to enable the wood to be fully penetrated, whereby it is softened, which facilitates the mechanical separation of the fibres, greatly improves the quality of the pulp, decreases the amount of power required to produce the pulp, and also increases the amount of pulp which may be produced.

However, we have found that under certain conditions, when this vacuum treatment is used it is possible at times to entirely eliminate the immersion treatment, that is, leaving the wood in the warm water, as the vacuum treatment so improves the penetration of the wood that the immersion treatment may be eliminated entirely or greatly shortened.

After the pulp has been so treated, the process follows that of the process set out in the above-mentioned patent, that is, after the above steps have been completed the wood is removed from the tank and is run through the usual or any form of pulp grinder, such as are now in use or'other form of disintegrating device, after which the pulp is screened and refined in the usual manner for the purpose of making paper or other articles of commerce.

As a pears from the above methods, the wood fibres are readily separated and by the elimination of resin pitch and so forth, and the softened condition of the wood, the grinding surfaces of the grindstonesor other disintegrating device which may be used for carrying out the process do not require as frequent dressing or attention as usual. Frequent dressing or sharpening causes wearing away of the grinding or disintegrating device, and this wear also causes wear upon the piping, pumps, valves, etc.,v of the system by abrasion, so that this is eliminated through our impro'ved'method. By reducing the acid in the wood through our process, less corrosion of the parts of the system will occur and the pulp and paper making felts and wires will remain cleaner than is ordinarily true, since impurities and extraneare obtained in our former patent but that by condensing the steam with cold water and forming a vacuum, the wood is more fineiso ' mer process, and lastly the time for the immersion process may be reduced and, under some conditions, entirely done away with.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. The treatment of wood for making pulp consisting in subjecting blocks or bolts of wood to an alkaline solution in a closed vessel, cooking the wood to remove oils and acids therefrom, and subjecting the wood to a vacuum to facilitate mechanical separation of the fibres, preparatory to grinding.

2. The treatment of wood for making pulp consisting in subjecting blocks or bolts of wood to an alkaline solution, applying steam pressure to the wood for the removal of oils and acids therefrom, subjecting the blocks or bolts to a vacuum, and washing the wood with warm water to remove extraneous matters and facilitate the mechanical separation of the fibres, preparatory to grinding.

3. The treatment of wood for making pulp consisting in subjecting blocks or bolts of wood to an alkaline solution, applying steam pressure to the wood to cook the same and remove oils and acids therefrom and then immersing the wood in-warm water for a sufficient period of time to remove extraneous matters and facilitate mechanical separation of the fibres of said wood, preparatory to grinding.

4. The treatment of wood for making pulp consisting in introducing blocks or bolts of wood to a closed tank, filling the tank with an alkaline solution, applying steam pressure within said tank and maintaining same therein according to the size and condition of the wood, removing gases and liquors from the tank, creating a vacuum within said tank for a suflicient period of time so that the heart wood will be thoroughly penetrated, and filling the tank with warm water to completely immerse the wood therein, preparatory to inding. 5. The treatment of wood for making pulp for corrugated boards and the like consisting in first introducing blocks of wood to a closed n tank, filling the tank with an alkaline solution, applying steam within said tank and maintaining the same therein for a predetermined length of time to thoroughly cook the wood, exhausting gases and recovering crude oils from said tank at predetermined intervals, draining all liquors from said tank,

forming a vacuum in said tank, and injecting weak liquor in the tank while the steam pressure is being maintained.

6. The treatment of wood for making pulp an alkaline solution, applying steam Within said tank and maintaining the same there in for a predetermined length of time to cook the wood, exhausting gases and recovering crude oils from said tank at predetermined intervals, draining all liquors from said tank, introducing cold water to the tank while the wood is under steam pressure to thereby condense the same and create a vacuum within the tank, draining ofi the water and refilling the tank with warm water, maintaining the temperature and pressure during the immersion process, the length of the immersion process being determined by the nature, size, and condition of the wood.

7. The treatment of wood for making pulp for paper without the admixture of pure chemical pulp which consists in placing blocks or bolts of wood in a closed tank, filling the tank with an alkaline solution, applying steam to cook the wood, exhausting gases and draining the tank, creating a vacuum within said tank, and again refilling the tank with warm water for a predetermined length of time.

8.. The treatment of wood for making pulp preparatory to grinding consisting in placing the wood in a tank with an alkaline solution therein, cooking the wood with steam,

In testimony whereof we aflix our signatures.

WILLIAM BRYDGES. SPOTTSWOOD C. FOSTER. 

